In plumbing installations, copper tubing is widely employed. In risers, used for connecting tubing to fixtures or tanks, the end of the copper tubing is shaped to form a bulb sealing surface and such bulb includes a shoulder permitting the tubing and thus the bulb sealing surface to be drawn into biting or sealing engagement with the fixture. The cost of such copper tubing and the cost of forming the same to permit the connection to such fixtures or tanks is substantial.
More recently, polybutylene has been approved for use in plumbing. Polybutylene is a relatively new polyolefin. Tubing or pipe made of polybutylene is normally joined by heat-fusion techniques, by mechanical compression, and by cold-flaring. Reference may be had to the Modern Plastics Encyclopedia, 1976-1977, page 49, for a discussion of polybutylene, its chemistry, properties, and grades.
In order to provide such polybutylene tubing with a bulb sealing surface or an end cap for such purposes, a variety of techniques have been employed. A common technique is to employ a separately molded bulb which is spun-welded to the O.D. of the end of a tube. Another technique is to form a flange on the O.D. of the tube and again to insert a separately molded neoprene or like concave washer on the flange for sealing purposes. Both such processes have cost and performance drawbacks. Both require separately molded parts which must be joined to the tubing in assembly operations. Moreover, a two-part tubing end cap or bulb sealing construction does not have the performance integrity or the expected useful life of the tubing itself. In a spun welding technique excessive clamping pressures may cause the loaded part to become dislodged or separated from the O.D. of the tubing and the interface of the parts provides a possibility of leakage. In the case of a neoprene or like washer employed on the O.D. of the tubing, the same interface leakage susceptibility is present. Moreover, a flange formed to receive the washer may itself create a point of weakness if excessive clamping pressures are employed. Further, neoprene washers are known to deteriorate with age and temperature exposure.